1. Field of the Invention
The present invention relates to a radiation thermometer for measuring continuously the temperature of molten iron such as molten pig iron or molten steel and a method of measuring the temperature of molten iron by using the radiation thermometer.
2. Discussion of Background
There is a strong demand of measuring continuously and stably the temperature of molten iron such as molten pig iron or molten steel in order to achieve automation and artificial intelligence (AI) control in the processes from pig iron making to steel making.
As a conventional technique of measuring the temperature of molten iron, there has been employed a method that temperature measurement is conducted intermittently and at short time intervals by immersing a disposal thermometer in which a thermocouple is sealed in a protecting tube made of quartz glass (an immersion type thermometer) at every 15-20 minutes, as a method of obtaining reliable values of measurement, for instance. However, the conventional method is complicated and troublesome, and it is not suitable for continuous temperature measurement of molten iron.
Further, as a method of continuously measuring temperature, there has been employed a method of measuring the surface temperature of the molten pig iron by a radiation thermometer. In such method, however, it was inavoidable that values of measurement often fluctuated to the lower temperature side since slag floating on the surface of the molten metal interrupts the radiation. Further, it was difficult to obtain reliable values of measurement by the radiation thermometer since barriers such as slag usually float on the surface of molten steel. Thus, there have been proposed no radiation thermometers for molten iron which are suitable for automation and AI control of iron making processes and which provide stably and continuously correct temperature measurement values.
In recent years, a thermocouple type thermometer for molten steel in which a protecting tube made of zirconium boride ceramics has been developed (Japanese Unexamined Patent Publication Nos. 31027/1989, 288738/1989 and 321326/1989).
Although the thermocouple type thermometer can be utilized for measuring temperature of molten iron, there still remains the problem that an error is produced in a measurement value due to deterioration of the thermocouple, and consumption of an expensive platinum-rhodium type thermocouple is unavoidable.